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Sigma SD14 Digital SLR with 14.1 MegaPixel Foveon Sensor

Part I

June, 2007

John E. Johnson, Jr.

 

Specifications:

● Interchangeable Lens Digital SLR Camera
● Sensor: Foveon
X3 CMOS; 14.1
   MegaPixels; 20.7mm x 13.8mm
● Aspect Ratio: 3:2
● Resolution: 4608 x 3072 Pixels
● ISO Range: 100 - 1,600
● Shutter Speeds: 30 sec - 1/4000 sec
● Flash Sync: 1/180 sec
● Files: JPEG, RAW
● Storage: Compact Flash
● Lenses: Sigma SA
● Dimensions: 4.2" H x 5.7" W x 3.2" D
  (w/o Lens)
● Weight: 2 Pounds with Battery (w/o
   Lens)
● MSRP: $1,596 USA w/o Lens

Sigma Photo

Introduction

A little more than two years ago, we reviewed the Sigma SD10 DSLR (Digital Single Lens Reflex) camera. It used a 10.2 megapixel Foveon sensor. I like the way Sigma names their cameras: for the megapixels of their sensors. As such, the SD14 has 14.1 megapixels.

The Design

Although 14 mp is quite a bit, it is not the resolution that makes this camera unusual. It's the design of the sensor itself.

Just about every digital camera out there, except for video cameras that use three sensors, has what is called the Bayer arrangement for its pixels, as shown in the diagram below.

Each pixel has a tiny color filter on top of it, either for red, green, or blue, and each colored pixel transmits color information for that color to the camera's electronic circuits for processing. Because the eye is more sensitive to green than to red or blue, there are two green pixels for each red or blue pixel.

The obvious problem with the Bayer arrangement is that the fine detail present on a red pixel is not the same as on the adjacent green or blue pixels, so this causes the final image not to be a sharp as it could.

Foveon - a company in Northern California - designed its digital sensor such that the red, green, and blue pixels are arranged columnar with relation to the light striking the sensor, rather than side by side as with the Bayer configuration. This is illustrated in the two diagram, shown below.

As a result, the fine detail can be much sharper. This arrangement in the way the three primary colors are recorded is the same as it is for color film, as shown below.

 

The sensor for the SD14 is the same size as for the SD10, but with more pixels. It is smaller than the full 35mm film space (24mm x 36mm) for conventional 35mm cameras and full frame DSLRs. This means you have to multiply the focal length of the lens by 1.7 to determine the equivalent visual field for the SD14 compared to a lens on a regular 35mm camera. So, if the lens on the SD14 is 28mm, the visual field is equivalent to the field given by a 48mm lens on a regular camera. In other words, if you like wide angle photography, you need to use a wider angle lens to get the same visual field as you would if you used a regular camera that has the full frame. There are a few full frame DSLRs out there, such as the Canon 5D that I use, but you are talking three grand and that is without any lens. Sigma, as well as other camera manufacturers, make specialized lenses that are optimized for the reduced film space in most DSLRs, so, except for one or two factors like noise - which I will get to in the bench tests - the point is almost moot.

The body of the SD14 is very similar to the SD10, save for some of the buttons being in different places.

Lenses use a bayonet mount (push in, twist to lock). Just inside the lens mount is an infrared filter, as seen in the photo below. This filter removes infrared light and only allows visible light to reach the sensor. It serves as a dust filter as well, so you just have to brush the dust off this filter to keep everything clean, instead of brushing the sensor (which is very delicate).

Another very useful feature with this filter is that it can be removed for infrared photography. The human eye sees light from deep blue to deep red, but we cannot see infrared. By removing the infrared filter, and using a special filter in front of the lens that allows only infrared light to enter, we can take infrared photos, which I will show you later.

All modern digital cameras have filters to remove infrared light, but they are usually part of the sensor construction, so you can't remove them. Although they are weak filters and you could take infrared photos by just extending the exposure, this is not the best way of taking such pictures. The SD14 is the only consumer DSLR out there right now that is easily converted for infrared photography (by taking out the filter).

The photo on the right shows the camera with the infrared filter removed. You can see the mirror in the center.

One caveat here: the infrared filter is very, very delicate, being made of thin glass. I broke one when I tried to put it back in because the plastic frame that holds it flexes. Sigma replaced it for me, but I suggest that you be extremely careful in taking it out and putting it back in.

Go to Part II.

Copyright 2007 Secrets of Home Theater & High Fidelity

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